Hidemaro Mori

Characterization of nociceptin hyperalgesia and allodynia in conscious mice

Intrathecal (i.t.) administration of nociceptin and high doses of morphine induced allodynia in response to innocuous tactile stimuli, and i.t. nociceptin evoked hyperalgesia in response to noxious thermal stimuli in conscious mice. Here we have characterized the nociceptin‐induced allodynia and compared it with the morphine‐induced allodynia and the nociceptin‐evoked hyperalgesia. Nociceptin‐induced allodynia was evoked by the first stimulus 5 min after i.t. injection, reached a maximum at 10 min, and continued for a 50 min experimental period. Dose‐dependency of the allodynia showed a bell‐shaped pattern from 50 pg to 5 ng kg−1, and the maximum effect was observed at 2.5 ng kg−1. Morphine‐induced allodynia reached the maximum effect at 15 min and declined progressively until cessation by 40–50 min. The dose‐response curve showed a bell‐shaped pattern, similar to that induced by nociceptin, with a maximum effect at 0.5 mg kg−1, five orders of magnitude higher than that of nociceptin. The allodynia evoked by nociceptin and morphine were dose‐dependently blocked by glycine, D(−)‐2‐amino‐5‐phosphonovaleric acid (D‐AP5, an N‐methyl‐D‐aspartate (NMDA) receptor antagonist), γ‐D‐glutamylaminomethyl sulphonic acid (GAMS, a non‐NMDA receptor antagonist) and methylene blue (a soluble guanylate cyclase inhibitor), but were not affected by muscimol (a γ‐aminobutyric acidA (GABAA) receptor agonist) and baclofen (a GABAB receptor agonist). Morphine did not inhibit forskolin‐stimulated cyclicAMP formation in cultured cells expressing the nociceptin receptor. Nociceptin‐induced hyperalgesia was evoked 10–15 min after i.t. injection. Nociceptin produced a monophasic hyperalgesic action over a wide range of doses from 5 fg to 50 ng kg−1. The nociceptin‐induced hyperalgesia was blocked by glycine only among the agents examined. None of the pain responses evoked by nociceptin and morphine were blocked by naloxone. These results demonstrate that, whereas the mechanisms of the nociceptin‐induced allodynia and hyperalgesia are evidently distinct, they involve a common neurochemical event beginning with the disinhibition of the inhibitory glycinergic response. Morphine may induce allodynia through a pathway common to nociceptin, but the nociceptin receptor does not mediate the action of high doses of morphine.

Autoantibodies to NMDA receptor in patients with chronic forms of epilepsia partialis continua

Background: Antibody-mediated and cytotoxic T cell-mediated pathogenicity have been implicated as the autoimmune pathophysiologic mechanisms in Rasmussen’s encephalitis. Methods: The authors investigated autoantibodies against the NMDA glutamate receptor (GluR) ε2 subunit and their epitopes in serum and CSF samples from 15 patients with chronic epilepsia partialis continua (EPC), 17 with West syndrome, 10 with Lennox–Gastaut syndrome, and 11 control subjects. Results: In 15 patients with chronic EPC, we detected NMDA-type GluR ε2 autoantibodies in histologically proven Rasmussen’s encephalitis (3/3 patients), clinical Rasmussen’s encephalitis (6/7 patients), acute encephalitis/encephalopathy (2/3 patients), and nonprogressive EPC (2/2 patients). Serum IgM autoantibodies were found in the early phase of EPC and became negative later in four patients. The autoantibodies were not detected in West syndrome, Lennox–Gastaut syndrome, or controls. Among 10 patients with histologically proven or clinical Rasmussen’s encephalitis, epitope analyses showed that the autoantibodies were predominantly against C-terminal epitopes and rarely against N-terminal epitope, with inconsistency in profile during the courses of disease. Epitope recognition spectrum of autoantibodies was broader in CSF than in serum, and the serum or CSF profile showed an increase in number of epitopes as disease progressed in some patients. Conclusions: The presence of autoantibodies against NMDA GluR ε2 suggests autoimmune pathologic mechanisms but is not a hallmark of Rasmussen’s encephalitis. Patients with Rasmussen’s encephalitis may have autoantibodies against several neural molecules, and these autoantibodies may be produced in the CNS after cytotoxic T cell-mediated neuronal damage.

Characterization of the glutamatergic system for induction and maintenance of allodynia

Glutamate is the main excitatory neurotransmitter in the central nervous system and has been shown to be involved in spinal nociceptive processing. We previously demonstrated that intrathecal (i.t.) administration of prostaglandin (PG) E(2) and PGF(2 alpha) induced touch-evoked pain (allodynia) through the glutamatergic system by different mechanisms. In the present study, we characterized glutamate receptor subtypes and glutamate transporters involved in induction and maintenance of PGE(2)- and PGF(2 alpha)-evoked allodynia. In addition to PGE(2) and PGF(2 alpha), N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), but not kainate, induced allodynia. PGE(2)- and NMDA-induced allodynia were observed in NMDA receptor epsilon 4 (NR2D) subunit knockout (GluR epsilon 4(-/-)) mice, but not in epsilon 1 (NR2A) subunit knockout (GluR epsilon 1(-/-)) mice. Conversely, PGF(2 alpha)- and AMPA-induced allodynia were observed in GluR epsilon 1(-/-) mice, but not in GluR epsilon 4(-/-) mice. The induction of allodynia by PGE(2) and NMDA was abolished by the NMDA receptor epsilon 2 (NR2B) antagonist CP-101,606 and neonatal capsaicin treatment. PGF(2 alpha)- and AMPA-induced allodynia were not affected by CP-101,606 and by neonatal capsaicin treatment. On the other hand, the glutamate transporter blocker DL-threo-beta-benzyloxyaspartate (DL-TBOA) blocked all the allodynia induced by PGE(2), PGF(2 alpha), NMDA, and AMPA. These results demonstrate that there are two pathways for induction of allodynia mediated by the glutamatergic system and suggest that the glutamate transporter is essential for the induction and maintenance of allodynia.

Inhibition of nociceptin-induced allodynia in conscious mice by prostaglandin D2

1 We recently showed that intrathecal administration of nociceptin induced allodynia by innocuous tactile stimuli and hyperalgesia by noxious thermal stimuli in conscious mice. In the present study, we examined the effect of prostaglandins on nociceptin‐induced allodynia and hyperalgesia. 2 Prostaglandin D2 (PGD2) blocked the allodynia induced by nociceptin in a dose‐dependent manner with an IC50 of 26 ng kg−1, but did not affect the nociceptin‐induced hyperalgesia at doses up to 500 ng kg−1. BW 245C (an agonist for PGD (DP) receptor) blocked the allodynia with an IC50 of 83 ng kg−1. 3 The blockade of nociceptin‐induced allodynia by PGD2 was reversed by the potent and selective DP‐receptor antagonist BW A868C in a dose‐dependent manner with an ED50 of 42.8 ng kg−1. 4 Glycine (500 ng kg−1) almost completely blocked the nociceptin‐induced allodynia. A synergistic effect on the inhibition of nociceptin‐evoked allodynia was observed between glycine and PGD2 at below effective doses. 5 Dibutyryl cyclic AMP, but not dibutyryl cyclic GMP, blocked the nociceptin‐induced allodynia with an IC50 of 2.9 μg kg−1. 6 PGE2, PGF2α, butaprost (an EP2 agonist) and cicaprost (a PGI receptor agonist) did not affect the nociceptin‐induced allodynia. 7 These results demonstrate that PGD2 inhibits the nociceptin‐evoked allodynia through DP receptors in the spinal cord and that glycine may be involved in this inhibition.

Central nociceptive role of prostacyclin (IP) receptor induced by peripheral inflammation

Prostacyclin (PGI2) is well known to play crucial roles in induction of edema and pain behavior in the periphery. In the present study, we investigated the central role of PGI2 in inflammatory pain. Intraplantar injection of carrageenan markedly induced the expression of prostacyclin receptor (IP receptor) mRNA with the maximum at 6 h, coincidently induction of the inducible form of cyclooxygenase (COX-2), although IP receptor mRNA was weakly expressed in the spinal cord of naive mice. Intrathecal administration of the IP agonist cicaprost induced mechanical hyper-algesia 6 h after carrageenan injection. These results suggest that PGI2 is involved in pain transmission at the spinal cord following expression of IP receptor mRNA induced by peripheral inflammation.

Stimulation of nitric oxide release from rat spinal cord by prostaglandin E2.

1 We recently demonstrated that intrathecal administration of prostaglandin E2 (PGE2) and PGF2α induced allodynia through a pathway that includes the glutamate receptor and nitric oxide (NO)‐generating systems from pharmacological studies. In order to clarify the involvement of NO in prostaglandin‐induced allodynia, we measured NO released from rat spinal cord slices by a chemiluminescence method. 2 PGE2 stimulated NO release from both dorsal and ventral regions all along the spinal cord. PGE2 stimulated the release within 10 min and increased it in a time‐dependent manner. 3 The PGE2‐induced NO release was observed at 100 nM–10 μM. PGF2α stimulated the release at concentrations higher than 1 μM, but PGD2 (up to 10 μM) did not enhance it. 4 17‐Phenyl‐ω‐trinor PGE2 (EP1>EP3) and sulprostone (EP1

Anti-nociceptive responses produced by human putative counterpart of nocistatin

b‐nocistatin is a heptadecapeptide produced from bovine prepronociceptin and blocks the induction of hyperalgesia and touch‐evoked pain (allodynia) by intrathecal administration of nociceptin or prostaglandin E2 (PGE2). Human prepronociceptin may generate a 30‐amino acid peptide different in length from b‐nocistatin. Here, we examine whether the human putative counterpart of nocistatin (h‐nocistatin) possessed the same biological activities as b‐nocistatin. Simultaneous intrathecal injection of h‐nocistatin in mice blocked the induction of allodynia by nociceptin and PGE2 in a dose‐dependent manner with ID50 values of 329 pg kg−1 and 16.6 ng kg−1, respectively. h‐nocistatin was about 10 times less potent than b‐nocistatin. h‐nocistatin also attenuated the nociceptin‐ and PGE2‐induced hyperalgesia. These results demonstrate that h‐nocistatin is biologically active and may be involved in the processing of pain at the spinal level in humans.

Characterization of nociceptin/orphanin FQ-induced pain responses in conscious mice: neonatal capsaicin treatment and N-methyl-d-aspartate receptor GluRε subunit knockout mice

Activation of primary afferent C fibers gives rise to spinal release of substance P and glutamate, and these mediators facilitate the cascade of nociceptive processing. We recently showed that intrathecal administration of nociceptin or orphanin FQ (hereafter called nociceptin) induced hyperalgesia to noxious thermal stimuli and allodynia to innocuous tactile stimuli applied to conscious mice. In the present study, we designed experiments to elucidate the pathways and mediators of nociceptin-evoked pain responses. Neonatal capsaicin treatment eliminated the induction of hyperalgesia and allodynia by nociceptin. Whereas this treatment markedly reduced the content of substance P in the spinal cord, it did not affect the nociceptin content or the expression of nociceptin receptors and GluRvarepsilon and GluRzeta subunits of N-methyl-D-aspartate receptors in it. The substance P antagonists CP96,345 and CP99,994 blocked the nociceptin-induced hyperalgesia, but not the allodynia. In contrast, the nociceptin-evoked allodynia, but not hyperalgesia, disappeared in N-methyl-D-aspartate receptor GluRvarepsilon1 subunit knockout mice. Both nociceptin-evoked hyperalgesia and allodynia were attenuated by morphine in a dose-dependent manner. Taken together, these results demonstrate that capsaicin-sensitive primary afferent fibers are involved not only in thermal hyperalgesia but also in tactile allodynia induced by nociceptin, but in different pathways; the former is mediated by substance P and the latter is mediated by glutamate through the N-methyl-D-aspartate receptor comprising the GluRvarepsilon1 subunit.

l-NAME, an inhibitor of nitric oxide synthase, blocks the established allodynia induced by intrathecal administration of prostaglandin E2

We recently reported that intrathecal (i.t.) administration of prostaglandin E2 (PGE2) to conscious mice induced allodynia, a state of discomfort and pain evoked by innocuous tactile stimuli. In the present study, we examined the effect of the PGE receptor EP1 subtype antagonist ONO-NT-012, the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801, and the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the allodynia. The PGE2-induced allodynia was blocked by simultaneous i.t. injection of ONO-NT-012, MK-801, or L-NAME. However, 5 min after i.t. injection of PGE2, the allodynia was significantly blocked by i.t. L-NAME, but not by i.t. ONO-NT-012 or MK-801. These results demonstrate that the PGE2-induced allodynia, once developed, does not require the continued agonist occupancy of EP1 and NMDA glutamate receptor sites.

Damaged Univent tubes.

The patient was a 62-yr-old, 158-cm, 58-kg man scheduled for surgery with a diagnosis of esophageal cancer. After placement of a 8.5-mm single-lumen cuffed Univent@ tube made of silicon, the built-in cuff was advanced into the right mainstem bronchus with the aid of fiberoptic bronchoscopy. The bronchial blocker cuff was inflated to permit one-lung ventilation that was confirmed by auscultation of the lungs. The patient was in a left semilateral decubitus position, and the operating table was rotated to the left according to the surgical procedure. During two-lung ventilation, analysis of arterial blood gases was normal, and pulse oximetry showed 99%-100% oxygen saturation. However, during one-lung ventilation, oxygen saturation decreased to 93%, and Pao, gradually decreased from 130 to 52 mmHg despite the inhalation of 100% oxygen. One-lung ventilation time was 90 min in total, and during this period, both lungs were ventilated manually a few times until oxygen saturation recovered to 100%. Surgery was completed in 6 h 20 min; the anesthesia time was 7 h 40 min. The patient entered the intensive care unit with the Univent@ endotracheal tube still in place. When the trachea was suctioned, using a fiberoptic bronchoscope, we found a foreign body at the proximal region of the left anterior segmental bronchus, and the object was removed. As it seemed to be a silicon fragment, the Univent@ endotracheal tube was replaced with a singlelumen tube, and we inspected the Univent@ tube carefully. The inner part where a slip joint (a tracheal tube connector) attached to the tube was broken, and the object that was removed from the patient’s bronchus fit perfectly into the defective area (Fig. 1). Neither atelectasis nor the foreign object was seen on chest radiograph taken immediately after the patient entered the intensive care unit.